Microcalorimetry, both isothermal and scanning, will be employed in the study of a wide range of processes and systems, including: (a) the phase transitions of various pure phospholipids such as methyl and fluorine substituted phosphatidylcholines (PC's), and PC's containing two different alkyl chains; the thermotropic behavior of phospholipid mixtures, such as dimyristoylphosphatidylglycerol and dimyristoylphosphatidylcholine; (b) the effect of various addenda, such as valinomycin, glucagon, apo-proteins from serum lipoprotein, and Beta-D-hydroxybutyrate dehydrogenase on the phase transitions of phospholipids; (c) processes involving proteins, such as the polymerization of the coat protein of tobacco mosaic virus; the binding of glucose and ATP to hexokinase; (d) biological processes such as phagocytosis. Many of these studies will be carried out in collaboration with scientists from other institutions. Stopped-flow kinetic observations on the reactions of the SH groups of tubulin in various states of aggregation will be made in an attempt at improved understanding of the assembly of microtubules.